Conventional mechanical stages for microscopes have manually actuable drive mechanism mounted below the table, with a coaxial arrangement of the drive means for the two directions of displacement. The transmission of the rotary actuation of the drive knobs is translated into table displacement via pinions which mesh with racks on individually displaceable table parts.
When scanning large-area objects, the user of such tables frequently desires to bring the table rapidly into an approximate desired position without time-consuming rotation of the drive mechanism, which operates with a very high reduction ratio.
A simple direct shifting of the table by hand is, however, not readily possible since the drive mechanism is characterized by friction which is necessary to assure stability of the table; this friction, in the context of the transmission-reduction ratio, makes a rather large expenditure of force necessary, whereby the racks or pinions could be damaged.
For rapid displacement of the table, it is already known to disconnect the drive mechanism from the table by means of an additional handle. Such devices are described, for instance, in German Pat. Nos. 3,025,974 and 3,037,710 and German Offenlegungsschrift application Nos. OS-3,027,461 and OS-3,037,741. For this purpose, friction-wheel gearing is interposed between the table and the drive mechanism, and for disconnection, the drive mechanism is either moved axially or the entire drive-mechanism housing is moved radially, so that both the drive-side and the driven-side friction wheels become disengaged.
The known solutions are, however, unsatisfactory, since, on the one hand, the drives should be relatively secure with respect to the table while, on the other hand, the engagement and disengagement process should take place easily so as to avoid accidential displacement of the table. Both of these requirements can be satisfied from a design standpoint only with difficulty or by relatively expensive measures.